If you pull the belt off the Y motor and then swap the motor X and Y axis at the Rambo board, and the problem transfers to the Y motor, you have a bad Rambo board. If the issue remains with the X axis, you have a short in the cable path, or a swapped pin.
The way a stepper motor works, is there are two coil loops that work together to turn the motor shaft, add force, and make the motor work properly. The first coil is pin 1 and 2, the second is pin 3 and 4 of the 4 pin motor connector block. If one of those two coil loops are cut anywhere between the Rambo than you will get a motor that doesn’t turn strongly. It will move some, but just weakly, and can fail to move sometimes and or grind. It will be easier to turn in the correct direction, and offer resistance if you try to turn it against the direction it wants to go, but not nearly as strong as it would normally turn.
If you instead have one of the two pins swapped, you end up with a magnet coil in opposition to the other one, which ends up basically making two magnets fight for control of the motor shaft. In that scenario you will hear a loud buzzing and the shaft will vibrate but not move much at all, and will be hard to turn either way.
Based on the symptoms you are seeing so far, and the fact that you have replaced the motor already, the issue is one of the following (in order of likelihood):
- You have one or more pins loose at a wire harness connection point. (where the motor attaches to the wire harness, where the harness attaches to the Rambo, etc.)
- You have one or more pins swapped in the wire harness (pin came out, got put back in the wrong spot)
- You have a physical wire issue on the wire harness (warranty service issue)
- You have a bad motor controller or pin block on the Rambo board itself.
- your printer is actually haunted.
- Your printer is actually haunted, but that’s not the problem and it’s really also just broken.
Edit, if it were the power supply you would be experiencing other issues. It’s also very unlikely that both motors are broken. You can test them by swapping them in on the Y axis.